Tilt-sensitive devices



March 3, 1970 A M. SQUIRE ETAL 3, 9

' TILT-SENSITIVE DEVICES ori im Filed' June 1. 1965 Inventor ALLAN MAURICE SQU/RE DONALD FULTON AL XAN ER MACLACH AN W Atlomey United States Patent 3,497,950 TILT-SENSITIVE DEVICES Allan Maurice Squire, Harpenden, and Donald Fulton Alexander MacLachlan, Surrey, England, assignors to British Aircraft Corporation Limited, London, England, a British company Original application June 1, 1965, Ser. No. 460,075, now abandoned. Divided and this application Sept 28, 1967, Ser. No. 671,351

Int. Cl. B23k 31/02 US. Cl. 29-622 1 Claim ABSTRACT OF THE DISCLOSURE A tilt sensitive device comprises a tubular body having a concave upper wall and contains an electrically conducting fluid and a non-conducting bubble; it has a central electrode and an end electrode on each side of the centre electrode; the length of the bubble is less than the distance between the two end electrodes. The electrodes are formed by flowing a conductive cement through holes in the walls and firing it, after which it is given a spongy surface.

This application is a divisional application from our application Ser. No. 460,075 filed June 1, 1965 and now abandoned.

This invention relates to manufacture of tilt-sensitive devices in which the departure of the device from the level position is indicated electrically.

A tilt-sensitive device according to the invention comprises a sealed envelope containing an electrically conducting liquid and a level responsive bubble of a fluid of differing conductivity and density, the envelope having an internal concave longitudinal surface which is smooth and uniform, the tube having also a central electrode rigidly supported midway between the ends of the concave surface in such a position that while the bubble of fluid is in contact 'with that concave surface the bubble cannot come into contact with that electrode, and having two end electrodes, one each side of the central electrode, rigidly supported at equal distances from the central electrode and each in a position which is at or near an end of the concave surface, the length of the bubble when in contact with the concave surface being considerably shorter than the distance apart of the two end electrodes, and the end and central electrodes having sponge surfaces.

The electrical resistance values between the central electrode and the end electrodes depend upon the position of the bubble in the tube and so their values are an indication of any departure of the device from a level position. These resistances may be measured by any suitable bridge-circuit, for example an AC. bridge including an amplifier.

Preferably the enevlope is internally barrel shaped or is a tube of uniform diameter which has been curved into an are, thereby forming an internal longitudinal concave surface.

The bubble may be of a fluid having a density greater than that of the electrically conducting liquid, in which case the concave surface with which it is in contact during use will be at the bottom of the device. Preferably, however, the bubble has a density less than that of the electrically conducting liquid and so the concave surface will be at the top of the device during use. The bubble fluid must not be miscible with the electrically conducting liquid to any appreciable extent. It may either be a liquid or a gas. The envelope is preferably constructed of glass of the borosilicate type, for example, as sold under the trade mark Pyrex. Preferably the electrolyte is a solution of lithium chloride in an alcohol such an ethanol or isopropanol. The bubble fluid may conveniently be air.

The electrodes have sponge surfaces. That is to say the area of surface of each electrode exposed to the electrolyte, this being the effective area of each surface, is substantially greater that the apparent surface area. The effective area may, for instance, be as much as several hundred times greater than the apparent area. Methods of producing electrodes with sponge surfaces are known.

The electrodes are rigidly supported in the envelope. In accordance with this invention, the device is made by a method which includes the steps of forming said electrodes by boring holes in the envelope, applying platinum resinate paint on the inside of the envelope in such a manner that the paint flows through the holes, and also applying paint on the outside of the envelope so that the paint which fills the holes, together with the local zones of paint inside and outside, forms conducting plugs, firing the paint, treating the paint electro-chemically to thereby provide a sponge surface on each plug towards the interior of the envelope, and attaching a lead to each plug externally of the envelope.

The advantages exhibited by tilt-sensitive devices made in accordance with the invention are due to the large effective area of the electrodes, and one of these advantages is that, for a given current, the current density at the electrodes is much less than at the electrodes of known devices having point or strip electrodes, so that polarisation effects are reduced or eliminated. The devices according to the invention thus have a much greater sensitivity than have tilt-sensitive devices of the prior art.

A further advantage is that a lower frequency may be applied to devices according to the invention than it has previously been possible to use. A convenient frequency is one of the order of 50 cycles per second. A further advantage is that the life of the devices according to the invention is, due to the large effective area of the electrodes, longer than the life of tilt-sensitive devices of the prior art.

It is found that by choosing a particular ratio for the volume of the electrically conducting liquid to the volume of the bubble it is possible to reduce the temperature coeflicient to a minimum. This ratio is conveniently found by experiment under the conditions under which the device is to be used and it will depend on the temperature effects on liquid conductivity, surface tension and the length of the bubble due to expansion or contraction of the liquid.

The invention will now be described with reference to the accompanying drawing, in which the single figure shows diagrammatically a side elevation of a tilt-sensitive device made in accordance with the invention. In this figure the curvature of the walls of the envelope is exaggerated in order that it should be more clearly seen.

The device illustrated in the figure consists of a glass envelope 111 the upper surface of which is curved con-- vexly so that there is an internal longitudinal concave surface. The envelope contains an electrolyte 112 comprising a solution of lithium chloride in ethanol and a bubble 113 of air. It has a central electrode 115 and end electrodes 116 and 117. These electrodes 115, 116 and 117 are formed by boring holes in the envelope 111 and applying platinum resinate paint on the inside of the envelope in such a manner that the paint flows through the holes, and paint is also applied on the outside of the envelope so that the paint which fills the holes, together with the local zones of paint inside and outside, forms conducting plugs. The paint is then fired and treated electrochemically in known manner to provide a sponge surface so as to increase the effective area of the electrodes. The effective area of the treated surface may be of the order of 500 3 times the effective area of the untreated surface. The leads 118, 119 and 120 are attached by soldering to the electrodes.

What we claim is:

1. In a method of making a tilt-sensitive device; said device comprising a sealed envelope containing an electrically conducting liquid and a level responsive bubble of a fluid of differing conductivity and density, the envelope having an internal concave longitudinal surface which is smooth and uniform, the envelope having also a central electrode rigidly supported midway between the ends of the wall opposite to the concave surface in such a position that while the bubble of fluid is in contact with that concave surface the bubble cannot come into contact with that electrode, and having two end electrodes, one on each side of the central electrode, rigidly supported on said' wall at equal distances from the central electrode and each in a position which is at or near an end of the wall opposite to the concave surface, the length of the bubble when in contact with the concave surface being considerably shorter than the distance apart of the two end electrodes; the improvement comprising the steps of forming said electrodes by boring holes in the envelope, applying platinum resinate paint on the inside of the envelope in such a manner that the paint flows through the holes, and also applying paint on the outside of the envelope so References Cited UNITED STATES PATENTS 2,416,887 3/1947 Tibbetts 29630XR 2,627,121 2/1953 Moyer et a1. 33 211 2,864,156 12/1958 Candy 29530 XR FOREIGN PATENTS 1,255,255 1/1961 France.

950,845 2/1964 England.

JOHN F. CAMPBELL, Primary Examiner R. CHURCH, Assistant Examiner US. Cl. X.R. 

